The life cycle of building-related greenhouse gas emissions makes up ~39% [1]of energy- and process-related emissions globally. These emissions can be divided into two types of primary contributions: ‘operational carbon’ (the emissions related to cooling, heating, lighting and powering our homes and buildings) and ‘embodied carbon’ (the emissions related to processing and manufacturing the materials used in construction). Current decarbonization efforts predominantly focus on operational carbon, however, greater attention is urgently needed to address the missing link: embodied carbon.

The vast majority of decarbonization efforts in the building sector have focused on reducing operational carbon, particularly by shifting to renewable energy sources and improving the energy efficiency of our buildings’ operations. This focus is reasonable in light of the fact that operational carbon currently makes up about three-fourths [2]of building-related emissions. And given the impressive advancements made to decarbonize our grids and implement energy-efficiency improvements like insulation and smart appliances, operational carbon mitigation has become relatively inexpensive. It is notable, however that as we strive to increase our building efforts to meet rapidly rising global demand, the carbon breakdown between operational and embodied carbon is expected to shift drastically, resulting in a contribution split of nearly 50/50  by 2050, as shown in the table below.

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Opportunities to mitigate embodied carbon are quickly emerging but, so far, lack scale and prioritization. One challenge is that, while operational carbon is contained to the energy associated with a home’s operations, embodied carbon is generated across all phases of a building’s life-cycle. This includes upfront emissions generated through the processing and production of building materials, in-use emissions stemming from infrastructure maintenance, repairs and renovations, and end-of-life emissions from deconstruction, demolition, and waste disposal. This dispersal of emissions across time and space can make it difficult to identify specific target areas for intervention.

That said, a good starting point means recognizing the significant carbon footprint associated with the manufacturing of concrete, steel, and aluminum. Concrete - the most widely produced material in the world - accounts for a shocking 7% of global emissions [3], almost three times the footprint associated with flying. This is due to the emissions associated with ‘Portland cement,’ the traditional binder that makes up concrete, which is produced by baking limestone, clay, and other raw materials into clinker at colossal temperatures using carbon-emitting kilns that run on fossil fuels. What sets cement production apart from other materials, though, is the carbon dioxide generated as a direct by-product of the chemical reaction that occurs when limestone becomes clinker. In other words, even if the kilns used to produce cement are fully powered by renewables, the inherent chemical process still generates significant carbon emissions.  

Over the past few years jurisdictions have begun mandating emissions reductions by cement manufacturers, incentivizing innovation around lower-carbon alternatives. These emerging alternatives typically focus on either powering the manufacturing plants using renewable energy, producing concrete in ways that require less cement, developing methods to permanently store the by-produced CO2 and prevent its release, or even altering the chemical reactions so as to avoid the generation of CO2 as a byproduct in the first place. One start-up called Brimstone is developing carbon-negative cement by replacing limestone with basalt and silicate rocks that don’t contain carbon. Another called Fortera is finding inspiration from coral reefs, effectively capturing and mineralizing the CO2 released by cement kilns into a cement-like material.

We must keep in mind that silver bullet solutions for the climate crisis do not exist, and low-carbon cement is just one option in a growing toolbox of solutions that should work together to target the building sector’s emissions from every angle. Other ideas focus on shifting from traditional, carbon-intensive construction materials to regenerative, bio-based materials that reduce emissions and support natural systems. Use of timber, for instance, avoids many of the emissions associated with producing man-made building materials and provides long-term carbon storage, though particular attention is needed to ensure it is harvested sustainably and in moderation to avoid devastation of our natural forests. Bamboo offers a promising opportunity given its rapid growth rate and mechanical strength, though the materials used to treat bamboo products need to be innovated to reduce their carbon impacts. I’m particularly excited about fungal mycelia as a bio-based alternative given their wide-ranging binding applications, though they come with their own sets of questions and trade-offs.

I think it’s particularly important to reflect on the fact that the building sector has not always centered around carbon-intensive and destructive methods. Until the late 20th century, buildings were, by and large, constructed using locally-sourced biomass and earth-based materials. And still today, communities throughout the global south continue to rely on these types of eco-friendly methods in harmony with nature conservation. Learning from the indigenous and local pioneers of sustainable housing and securing their positions as leaders and decision-makers in the sustainable housing transition is critical to ensuring housing solutions that center equity and endure in the long-run.